Micellization Behavior Of Pluronic Block Copolymers In Aqueous Solution And Its Applicaton On Drug Carrier

Block copolymers with hydrophilic and hydrophobic segments in particular have been a rich field of research due to the structural diversity on self association in solvents selective for one block. Water-soluble poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) block copolymers are nonionic macromolecular surfactants, available commercially as Pluronics. Recently, the micellization of these copolymers has been focused because of a strong interest in Pluronic micelles as drug carriers. However, micellization of Pluronic copolymers is very complex compared with those conventional surfactants.The micellization of Pluronic amphiphilic block copolymers in selective solvent(water), was characterized by different methods such as the surface tension measurements, flurescene probe technique, dynamic light scattering(DLS) and Transmission Electron Microscope(TEM). The results showed several factors such as molar mass, composition, concentration of amphiphilic block copolymer, addition of inorganic salts and temperature play a key role in aggregation behavior, size and shape of microscopic self-assembled structures. Some results are as follows: (1)Temperature/polymer concentration/salt dependent aggregation behavior of L35 was observed by surface tension measurements. The data on critical micelle concentration(CMC) were reported. CMC values decreased significantly with the addition of KC1 while CMC values increased with the addition of KI, They have been spoken as salting-out and salting-in effects, respectively.(2)The micellization of the Pluronic copolymers F127 above critical micelle concentration(CMC) was detected by the flurescene probe technique. The results shown that CMC decreased with PEO content with the same molecule mass of hydrophobic segment at the certain temperature. For a given contration, CMC decreased with temperature.Besides, the flurescene probe technique with pyrene as a probe molecule shown that hydrophobic substance could effectively enrich into the hydrophobic core of micelles, which proved its application as a drug carrier.(3)The sizes of the self-assembly micelles of the Pluronic block copolymers and the effects were studied by dynamic light scattering (DLS) above the CMC, The micelle sizes were largely influenced by the hydrophobic chain content in the copolymer and the copolymer concentration in the aqueous solution. At the certain temperature, The size of micelle increased with PEO content with the same molecule mass of hydrophobic chain. And decreased with the concentration of Pluronic copolymer and then remained nearly constant. The dual effect of temperature increase on an increased aggregation number and a decreased micelle hydration makes it complex for the micelle size of F127 and P123. The addition of NaCl decreased the micelle size but independent with the concentration.(4)TEM observation indicated that micelles in size of 15-35 nm with a spherical morphology.(5)Polymer micelles were prepared by dialysis method with Pluronic block polymer P123 as the carrier material. The size of the micelles was in nanoscale and the size distribution was narrower. The morphology of the drug-loaded micelles was investigated by transmission electron microscopy. The drug-loaded micelles showed a sphere with inner core and outer shell. The amount of drug-loaded and release were investigated by UV-visible spectrophotometer (UV). Any initial burst release was not observed in the release pattern of all the samples.